Looks like an aluminum frame. It also looks like only one side of the tube is crushed, meaning that the head tube may still be in alignment.

My simple fix would be to first insure that the head tube is in alignment. I would then strip off all the paint from the down tube and inspect the tube inside and out for cracks. I would then take a half round sleeve of aluminum and Alumiweld it onto the out side of the tube.

Just a thought.

It certainly would look better then using a piece of angle iron the length of the tube fixed in place with hose clamps... Ha